SQL Server – Enabling FileStream after a DB has been created

To add FS support to existing database just create a new filegroup, then add the fs file;

alter database YourDatabase
add filegroup fsGroup contains filestream;
go

alter database YourDatabase
add file
  ( NAME = 'fsYourDatabase', FILENAME = 'c:\<your_file_path>'
   )
to filegroup fsGroup;
go

More here: BOL Link

And definitely read everything Paul Randal has written about filestream: link